1. Field of the Invention
The present invention relates to a stereoscopic display apparatus.
2. Description of the Related Art
A stereoscopic image display apparatus capable of displaying a motion image, i.e., a so-called 3D display, is available in a variety of schemes. Particularly, in recent years, a demand increases for a scheme of a flat panel type that does not require exclusive eyeglasses. Among stereoscopic motion image display apparatuses of this type, a scheme that utilizes the principle of hologram is difficult to display a full color motion image. Another scheme in which a beam control element controlling a beam from the display panel and directing the beam toward the observer is set immediately in front of a pixel position-fixed display panel (display device) such as a direct viewing type or projection type liquid crystal display apparatus, or a plasma display apparatus allows to display a full color motion image comparatively easily.
Generally, the beam control element is also called a parallax barrier, and controls the beam so that different images can be seen depending on the angle even at one position of the beam control element. More specifically, when providing only right-and-left parallax (horizontal parallax), a slit or a lenticular sheet (cylindrical lens array) is used. When including top-and-bottom parallax (vertical parallax) as well, a pinhole array or a lens array is used. Schemes that employ a parallax barrier are further classified into a binocular scheme, a multi-view scheme, a super-multi-view scheme (the super-multi-view conditions for the multi-view scheme), and integral photography (to be also referred to as IP hereinafter). These basic principles are almost identical to those invented about 100 years ago and have been employed in stereoscopic photography.
Among these schemes, the characteristic feature of the IP scheme resides in that it provides high degrees of freedom for the viewpoint position and enables stereoscopic vision easily. The 1D IP scheme that includes only horizontal parallax and does hot include vertical parallax can implement a high-resolution display apparatus comparatively easily, as is described in SID04 Digest 1438 (2004). In contrast to this, with the binocular scheme or the multi-view scheme, the range of the viewpoint position where stereoscopic vision is possible, i.e., the viewing area, is narrow, and the observer cannot see the image well. However, the binocular scheme or the multi-view scheme has the simplest arrangement as the stereoscopic image display apparatus, and can generate a display image readily.
In a direct viewing type autostereoscopic display apparatus using such a slit or a lenticular sheet, the periodic structure of the openings of the beam control element interferes with that of the pixels of the flat panel display apparatus to generate moiré or color moiré easily. As a countermeasure for this, a method of obliquely inclining the extending directions of the openings of the beam control element, i.e., a slanted lens, is known. This method, however, displays longitudinal lines in a zigzag manner when displaying a stereoscopic image to particularly result in poor character display quality. A vertical lens in which the extending directions of the openings of the beam control element are not inclined has no problem in the character display quality. To solve the color moiré, however, the color arrangement of the elemental image display must comprise a mosaic array or a lateral stripe array. To solve the moiré, the beam from an adjacent sub-pixel must be fused appropriately by, e.g., a method of adding a diffusion film between the elemental image display and the lenticular lens (JP-A 2005-86414 (KOKAI)). Addition of the diffusion film, however, scatters the external light to decrease the brightness contrast. Known methods of appropriately fusing the beam from the adjacent sub-pixel in the case of the vertical lens include a method of arraying sub-pixels to form a delta array (Japanese Patent No. 3027506), a method of forming parallelogrammic sub-pixel openings so that adjacent pixels overlap (PCT(WO) 10-505689), and a method of making the sum of the opening ratios of the sub-pixels in the longitudinal direction to a constant value (Japanese Patent No. 3525995). However, not only to solve the moiré but also to achieve continuous motion parallax as in the 1D IP scheme, with the conventional methods, the fusion of the beam from the sub-pixel is insufficient.
As described above, in the conventional stereoscopic display apparatus in which the beam control element is set vertically, moiré that interferes with display tends to occur readily to make it difficult to obtain continuous motion parallax.